Figure 9. (a) Purity (A620/A280) and (b) APC and P-PC yield recovered after VFD-ATPS processing at various speeds of rotation28, (c) conversion levels of substrates increase dramatically by swapping from non-covalent to covalent attachments, (d) optimized symmetrical amine-glutaraldehyde cross-linker for β-glucosidase applied for phosphodiesterase and alkaline phosphatase, with excellent stability after processing over ten hours, (e) β-glucosidase solution recycled, with the last sample tube having a similar substrate transformation to the first, (f) >20% catalytic activity for enzyme-immobilized tubes without buffer after being stored for one month56, (g) optimization of processing parameters (ratio of biomass to methanol, catalyst concentration, reaction time and rotational speed in rpm) for VFD-mediated dry biomass processing in confined mode. (h) TEM image (inset 10 nm scale bar), (i) SEM image, and (j) AFM image of P4C6-carboplatin host-guest vesicles after VFD processing, with (k) collapsed vesicle’s sectional height profile and host-guest complex elemental mapping with energy-filtered transmission electron microscopy for (l) unfiltered, (m) carbon, and (n) platinum49. (a-b) Reproduced with permission28. Copyright 2016, American Chemical Society. (c-f) Reproduced under the terms of the CC BY 3.0 license56. Copyright 2016, Royal Society of Chemistry. (g) Reproduced with permission53. Copyright 2018, Elsevier. (h-n) Reproduced under the terms of the CC BY 4.0 International license49. Copyright 2015, Springer Nature.
Recently, aggregation induced-emission luminogens (AIEgens) with high emission efficiency in the aggregated state, excellent photo-stability, and increased sensitivity have become one of the most promising nanoprobes for both material and process characterizations due to their flexibility, versatility, and robustness when compared to other strategies. The most frequently used approach to preparing AIEgen particles is precipitation. Without proper mixing under shear, AIE particles will be distributed in various sizes, affecting their ultimate brightness and applications. In the inaugural attempt for VFD-mediation of AIEgen size, controlling the size and shape of AIEgens was possible, impacting their fluorescence (FL) properties57. By increasing both concentration and rotational speed during the preparation of a particular AIEgen, tetraphenylethylene (TPE), the particle size was controlled and significantly reduced, with the smaller particles increasing the brightness. The ability of the VFD to produce AIEgens <10 nm in size with tunable FL intensities directly from a 90% solvent/antisolvent (SA) ratio at the VFD rotational speed of 5000 rpm is shown in Figure 10. In traditionally prepared TPE particles, a 40-times increase in the fluorescent maxima had been observed at the SA ratio of 95% compared to that of TPE particles prepared at the SA ratio of 80%. At SA ratios < 80%, the associated emissions had been zero. Surprisingly, it was found that VFD-derived solutions of TPE particles were fluorescent at the SA ratios < 80% (down to the SA ratio = 40%). At constant rotation speeds above 1000 rpm, the SA ratio increased to fluorescent maxima and maximum relative intensity. The highest maximum relative intensity for VFD-derived TPE particles was about 190 times greater for the SA ratio and rotation speed of 90% and 5000 rpm, respectively. Although other approaches, including multi-channel and microfluidic methods, had been unable to produce AIEgens <80 nm in size, use of the VFD provides a unique strategy to tune the size and control the FL property of AIEgens, which are important properties for different applications. As an advantage of size reduction, the direct diffusion of NPs within a cell or in a single-celled organism opens new opportunities for biological and material studies.
In another study, TPE-2BA AIEgen, a derivative of tetraphenylethylene with two boronic acid groups, was physically coupled with a commercially available hyperbranched polymer (HBP; bis-MPA polyester-64-hydroxyl; generation 4) using VFD58. Significant differences in FL intensity were found for the AIE–HBP (HBP concentration = 1 mM) at different SA ratios, as shown in Figure 10. The FL intensity increased 32-fold with the SA ratio = 90% compared to the SA ratio of 40%. Negligible changes in particle size in the VFD-driven AIE-HBP particles were reported compared to those prepared without VFD. The formation of AIE-HBP under shear stress increased AIE molecules’ penetration within the HBP structure, leading to significantly brighter AIE-HBP particles. It was reported that at the SA ratio = 90%, the average particle size for the traditionally prepared AIE-HBP was approximately 150 nm, with a relative FL intensity of 38 times greater than that of TPE-2BA alone. When the VFD was used, the particle size of the AIE-HBP was reduced to approximately 80 nm, and the relative FL intensity became 73 times greater. The formation of a smaller AIE-HBP complex containing more AIE molecules within the HBP molecule structure might be the reason for that observation. The authors concluded that, with the employment of a VFD, it was possible to form an AIE-HBP complex less than 100 nm in size under optimized conditions. This later resulted in the fabrication of fluorescent hydrogels with enhanced mechanical properties, and no sign of failure was observed in the hydrogel containing AIE-HBP (1 mM) over 800% strain.